When RIPA is sent into the newly discovered vertical drift, a mysterious malfunction nearly wipes out Jay as he tries to raise the roboti investigator up into the draft. After a few tense moments, RIPA is powered off, hoisted back down and inspected. Patrick discovers she needs new parts that must be shipped in, leaving her out of commission for the moment.
With the new drift on hold, Greybeard and Jamol head to the Western Tunnel to assay their gold prospects there. Strange noises and the sounds of other miners leave them spooked but, thankfully a quick eyeball assay reveals some gold, prompting the crew to blast deeper into the Western Tunnel.
Kristen discovers a visual pattern to the hauntings in the surrounding area: a series of straight lines. Chinese ghosts are said to travel in straight lines until they reach their home, so it's possible the hauntings could be connected to the spirits of the dead Chinese miners. She suggests a town-wide overnight investigation to test her theory.
Patrick and Kristen set up cameras throughout the town, aimed at some of Sumpter's most active locations, including the dredge, bed and breakfast, and the Elkhorn Saloon. They also have a camera pointed at the mine on the mountain. They enlist the help of Jay's son Ashton, an aspiring paranormal investigator himself, to man the control center and monitor all four video feeds while Kristen and Patrick conduct investigations at each site.
As Kristen and Patrick explore the dredge, their most active site besides the mine from last season, Ashton radios them about a strange shadow figure that has appeared on the cameras. When they go to investigate, it quickly dissipates. A few minutes later, Ashton experiences an encounter of his own at command central as loud banging noises sound around him. As Kristen and Patrick continue their investigation, Ashton again radios them about a strange visual anomaly seen on the video feeds.
They find an anomaly identical to the same glitch they saw following Jay in the mine. The next morning, they analyze the footage further to discover the glitch travels from all four points monitored in town to each of the cameras in the mine, heading deeper into the mountain, as though something was walking in a deliberate path, suggesting an intelligent haunting.
Stan comes to Kristen and Patrick with news of another mine out in Arizona experiencing paranormal events. He suggests taking a trip out there to check it out, since the Arizona climate allows for mining year-round as opposed to the short mining season out on the Elkhorn Mountain. If it's as rich in gold as Stan's contact describes, it could be a far more promising venture for the crew. Kristen agrees to head out with Stan while Patrick stays back in Sumpter. Eddie will take the lead as foreman in Stan's absence.
Kristen and Stan arrive at the Octave Mine in Congress, Arizona. This mine was once a high producer of gold and silver during the Gold Rush era, but had been nearly forgotten about since World War II. New mine owner Adam has already lost two mining crews spooked by strange sights and sounds within these 25 miles of tunnels, some attributing it to a local legend of the Blue Devil of Octave. The trio heads into the old mine to take a look for themselves.
While the mine needs substantial rehab work, Stan's early assessments suggest a promising venture. But then, a series of three distinct knocks from deep within the mine stops them in their tracks. Kristen's EMF detector starts registering high readings when nothing should be setting it off that far into the ground. More strange sounds take them deeper underground as they try to find the source, but come up empty-handed when they end up in a dead end with only strange markings on the walls. Kristen suggests conducting a more thorough investigation.
Back at the Crescent, Patrick meets with a local geologist who can offer more insight about the kind of minerals and rocks that could be harboring and activating paranormal energies in the mine. Patrick then reviews the evidence from their overnight town-wide investigation with the miners; Eddie only wants to know if it's safe to continue, as he's focused on the bottom line while Stan's away.
With RIPA finally repaired and back online, they hoist her back up into the vertical drift to take a look around. The initial inspection reveals some promising quartz veins, but as she presses further, she comes across something no one expected to find: An old wooden bulkhead sealing off the rest of her path.
Kristen sees the opening in the side of the mountain for herself and makes a startling realization about the way the mine aligns with Baker City.
In this shocking season finale, the miners finally approach the mother lode as Patrick and Kristen reveal the final shocking pieces of the paranormal puzzle.
Stan and Eddie check in with mine owner Larry to outline their prospects for what little remains of the mining season.